xfs: simplify inode to transaction joining

Currently we need to either call IHOLD or xfs_trans_ihold on an inode when
joining it to a transaction via xfs_trans_ijoin.

This patches instead makes xfs_trans_ijoin usable on it's own by doing
an implicity xfs_trans_ihold, which also allows us to drop the third
argument.  For the case where we want to hold a reference on the inode
a xfs_trans_ijoin_ref wrapper is added which does the IHOLD and marks
the inode for needing an xfs_iput.  In addition to the cleaner interface
to the caller this also simplifies the implementation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

diff --git a/fs/xfs/xfs_bmap.c b/fs/xfs/xfs_bmap.c
index ff8675b..e038965 100644
--- a/fs/xfs/xfs_bmap.c
+++ b/fs/xfs/xfs_bmap.c
@@ -3751,9 +3751,10 @@
 		ip->i_d.di_aformat = XFS_DINODE_FMT_EXTENTS;
 	}
 	ASSERT(ip->i_d.di_anextents == 0);
-	IHOLD(ip);
-	xfs_trans_ijoin(tp, ip, XFS_ILOCK_EXCL);
+
+	xfs_trans_ijoin_ref(tp, ip, XFS_ILOCK_EXCL);
 	xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
+
 	switch (ip->i_d.di_format) {
 	case XFS_DINODE_FMT_DEV:
 		ip->i_d.di_forkoff = roundup(sizeof(xfs_dev_t), 8) >> 3;